Human activity has helped accelerate global warming, which has caused the melting of the tundra's permafrost and an invasion of plant and animal species from the south. This affects native species that are adapted to sub-zero climates, as well as the people who depend on these natural resources.
Permafrost is permanently frozen ground. In North America, it covers 85 percent of Alaska and roughly 55 percent of Canada. It is normal for permafrost to thaw an inch or two during the summer in areas that aren't snow covered year-round. This allows small plants like wild-flowers and lichen to grow, which feeds the wandering caribou herds.
Permafrost is filled with organic material, some of it thousands of years old. When permafrost melts, that matter decomposes. That puts more carbon dioxide and methane into the atmosphere, adding to global warming. Invasive plants may also move into the former permafrost areas, possibly overpowering native plant species. Fewer lichen plants means fewer caribou.
Proof that animal species are migrating from the south exists in a new hybrid bear. As the pack ice continues to melt, polar bears are spending more time on land. Grizzly bears, attracted by the warming conditions, are ranging farther north than before. Polar bears and grizzly bears are mating, creating a hybrid species, locally called a "grolar" or "polar grizz."